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Beta Amyloid Aggregation Inhibitors: Small Molecules as Candidate Drugs for Therapy of Alzheimers Disease
Abstract and Figures
The progressive production and subsequent accumulation of β-amyloid (Aβ), a proteolytic fragment of the membrane-associated amyloid precursor protein (APP), plays a central role in Alzheimer's Disease (AD). Aβ is released in a soluble form that may be responsible for cognitive dysfunction in the early stages of the disease, then progressively forms oligomeric, multimeric and fibrillar aggregates, triggering neurodegeneration. Eventually, the aggregation and accumulation of Aβ culminates with the formation of extracellular plaques, one of the morphological hallmarks of the disease, detectable post-mortem in AD brains. In this review we report the known structural features of amyloid peptides and fibrils, and we give an overview of all small molecules that have been found to interact with Aβ aggregation. Deeper knowledge of the mechanism leading to amyloid fibrils along with their molecular structure and the molecular interactions responsible for activity of small molecules could supply useful information for the design of new AD therapeutic agents.
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... Tabla 1-Valores de pIC 50 calculados y pIC 50 experimentales para la base de datos de compuestos con actividad antiagregante del péptido βA 1-42 (Serie 1). [21][22][23] Para obtener información de la región teórica del espacio químico, definida por los descriptores del modelo, se determinó el dominio de aplicabilidad (DA). Este es "el rango dentro del cual el modelo tolera una nueva molécula", y se define como un área dentro de los límites +2 y -2 para los residuales estandarizados y un umbral del valor de influencia para la actividad inhibitoria. ...
... Estructuras químicas de los 24 compuestos utilizados en la confección del modelo QSAR para la predicción de la actividad antiagregante del péptido βA 1-42 (Serie 1).[21][22][23] A) Farmacóforo; B) Compuestos de la Serie 1 Estructuras químicas de los 32 compuestos utilizados en la confección del modelo QSAR para predecir la actividad inhibitoria de la enzima AChE (Serie 2).[24,25] ...
Alzheimer's disease (AD) is a neurological disorder characterized by progressive memory loss due to biochemical processes of multifactorial origin. This leads to the disruption of neuronal synapses and, as a consequence, to dementia. In the present work, structure-activity relationship and molecular docking studies were performed on two series of compounds with activity against two therapeutic targets for AD: with anti-β-amyloid peptide aggregation effect and with inhibitory activity of the enzyme acetylcholinesterase. A significant and predictive model of 50 % inhibitory activity dependence (IC50) was obtained for each series. The molecular docking results predicted the form and mode of interaction of the compounds with each of the targets studied.
... Therefore this model could in principle be expanded to also simulate the impact of novel amyloid therapies-many already in early clinical development-with different targets for instance focused solely on oligomers, 24 gamma-secretase modulators, 25 or with small molecules affecting the aggregation rate of Aβ species. 26,27 Based on the consensus that amyloid antibody therapy is best terminated after reaching amyloid negativity, we first simulated the time to Along the same lines, the virtual patient trial suggests that at 18 months, 78%, 72%, and 57% respectively of patients in the donanemab, lecanemab, and aducanumab trial were amyloid-negative. This is in accordance with reported clinical data of 71% for donanemab, 31 >75% ...
INTRODUCTION
Addressing practical challenges in clinical practice after the recent approvals of amyloid antibodies in Alzheimer's disease (AD) will benefit more patients. However, generating these answers using clinical trials or real‐world evidence is not practical, nor feasible.
METHODS
Here we use a Quantitative Systems Pharmacology (QSP) computational model of amyloid aggregation dynamics, well validated with clinical data on biomarkers and amyloid‐related imaging abnormality–edema (ARIA‐E) liability of six amyloid antibodies in clinical trials to explore various clinical practice challenges.
RESULTS
Treatment duration to reach amyloid negativity ranges from 12 to 44, 16 to 40, and 6 to 20 months for lecanemab, aducanumab, and donanemab, respectively, for baseline central amyloid values between 50 and 200 Centiloids (CL). Changes in plasma cerebrospinal fluid Aβ42 and the plasma Aβ42/ Aβ40 ratio—fluid biomarkers to detect central amyloid negativity—is greater for lecanemab than for aducanumab and donanemab, indicating that these fluid amyloid biomarkers are only suitable for lecanemab. After reaching amyloid negativity an optimal maintenance schedule consists of a 24‐month, 48‐month and 64‐month interval for 10 mg/kg (mpk) lecanemab, 10 mpk aducanumab, and 20 mpk donanemab, respectively, to keep central amyloid negative for 10 years. Cumulative ARIA‐E liability could be reduced to almost half by introducing a drug holiday in the first months. For patients experiencing ARIA‐E, restarting treatment with a conservative titration strategy resulted in an additional delay ranging between 3 and 4 months (donanemab), 5 months (lecanemab), and up to 7 months (aducanumab) for reaching amyloid negativity, depending upon the timing of the incident. Clinical trial designs for Down syndrome patients suggested the same rank order for central amyloid reduction, but higher ARIA‐E liability especially for donanemab, which can be significantly mitigated by adopting a longer titration period.
DISCUSSION
This QSP platform could support clinical practice challenges to optimize real‐world treatment paradigms for new and existing amyloid drugs.
... The determination of TC degradation intermediates in the Fe/KBC800/PS system was conducted using UHPLC-MS/ MS. Three possible degradation pathways, along with their corresponding intermediates and conversion processes, are depicted in Fig. 4. The molecular structure of TC contains conjugated double bonds, aromatic rings, phenol groups, and other electron-rich groups, which can react with ·OH to generate intermediates, particularly double bonds within TC molecules (Re et al. 2010). In this investigation, 7 kinds of conversion products were detected through mass spectrometry, with respective m/z values of 491, 309, 427, 399, 279, 242, and 186. ...
The release of antibiotics has attracted wide attention due to their abuse and discharge. How to remove these emerging contaminants is an urgent need to be solved. In the present study, sludge-based biochar combining chitosan and iron oxide was prepared via municipal sewage sludge. The novel biochar modified with chitosan and iron oxide exhibited satisfying performance in eliminating antibiotics from water. The application of modified biochar combined with activated persulfate (PS) showed a remarkable removal efficiency of 96.98% for tetracycline (TC). Analysis of the surface characteristics of the modified biochar showed the presence of structural defects, dispersed iron oxides, abundant functional groups, a porous structure, and a relatively stable crystal structure. These characteristics attributed significant importance to facilitating the degradation of TC. A series of experimental conditions including preparation temperature (600–900 ℃), reaction temperature (15–45 ℃), contaminant concentration (30–180 mg/L), adsorbent usage (0.1–1 g/L), pH (2–10), and persulfate addition concentration (1–5 mmol) were conducted. The results revealed that the highest removal efficiency was achieved at 96.98% under the conditions of TC concentration at 30 mg/L, reaction temperature at 35 ℃, pH of 4, adsorbent addition amount of 0.6 g/L, and PS concentration of 2 mmol, respectively. Three degradation pathways and seven intermediate products of TC were proposed. Therefore, our study provides a promising approach for developing effective removal of antibiotic pollutants.
... Further, the ApoE expression in a 1 month period was evaluated, in which the RVG-NV-NPs group maintained a significantly higher concentration of ApoE than the PBS group (P < 0.001, Figure 3m,n). Previous studies have shown that increase of ApoE in the brain results in reduced Aβ in an animal model of AD. 45 Taken together, these results suggest that the RVG-NV-NPs mediate the highly effective brain delivery of drugs, RXR activation, and upregulation of ApoE expression in APP/PS1 mice, which promises its potential in AD therapy. ...
Effective drug delivery in the central nervous system (CNS) needs to have long blood-circulation half-lives, to pass through the blood-brain barrier (BBB), and subsequently to be taken up by target cells. Herein, a traceable CNS delivery nanoformulation (RVG-NV-NPs) is developed by encapsulating bexarotene (Bex) and AgAuSe quantum dots (QDs) within Lamp2b-RVG-overexpressed neural stem cell (NSC) membranes. The high-fidelity near-infrared-II imaging by AgAuSe QDs offers a possibility of in vivo monitoring the multiscale delivery process of the nanoformulation from the whole-body to the single-cell scale. It was revealed the synergy of acetylcholine receptor-targeting of RVG and the natural brain-homing and low immunogenicity of NSC membranes prolong the blood circulation, facilitate BBB crossing and nerve cell targeting of RVG-NV-NPs. Thus, in Alzheimer's disease (AD) mice, the intravenous delivery of as low as 0.5% of oral dose Bex showed highly effective up-regulation of the apolipoprotein E expression, resulting rapid alleviation of ∼40% β-amyloid (Aβ) level in the brain interstitial fluid after a single dose administration. The pathological progression of Aβ in AD mice is completely suppressed during a 1 month treatment, thus effectively protecting neurons from Aβ-induced apoptosis and maintaining the cognitive abilities of AD mice.
... Amyloid-β (Aβ) aggregates in the brain of patients with Alzheimer's disease (AD) are considered the pathological and biological hallmarks of this neurodegenerative disorder [24]. Thus, drug candidates have been discovered to inhibit and reverse the Aβ aggregation process [25]. To investigate whether our compounds, succinyl glyco-oxydifficidin (1) and succinyl macrolactin O (2), inhibit and/or reverse Aβ aggregation, we performed two different types of assays, inhibition and dissociation, utilizing a high throughput screening platform we recently developed [26]. ...
Two new glycosylated and succinylated macrocyclic lactones, succinyl glyco-oxydifficidin (1) and succinyl macrolactin O (2), were isolated from a Bacillus strain collected from an intertidal mudflat on Anmyeon Island in Korea. The planar structures of 1 and 2 were proposed using mass spectrometric analysis and NMR spectroscopic data. The absolute configurations of 1 and 2 were determined by optical rotation, J-based configuration analysis, chemical derivatizations, including the modified Mosher’s method, and quantum-mechanics-based calculation. Biological evaluation of 1 and 2 revealed that succinyl glyco-oxydifficidin (1) inhibited/dissociated amyloid β (Aβ) aggregation, whereas succinyl macrolactin O (2) inhibited Aβ aggregation, indicating their therapeutic potential for disassembling and removing Aβ aggregation.
Prime editing shows potential as a precision genome editing technology, as well as the potential to advance the development of next-generation nanomedicine for addressing neurological disorders. However, turning in prime editors (PEs), which are macromolecular complexes composed of CRISPR/Cas9 nickase fused with a reverse transcriptase and a prime editing guide RNA (pegRNA), to the brain remains a considerable challenge due to physiological obstacles, including the blood–brain barrier (BBB). This review article offers an up-to-date overview and perspective on the latest technologies and strategies for the precision delivery of PEs to the brain and passage through blood barriers. Furthermore, it delves into the scientific significance and possible therapeutic applications of prime editing in conditions related to neurological diseases. It is targeted at clinicians and clinical researchers working on advancing precision nanomedicine for neuropathologies.
Alzheimer's disease (AD) is an onset and incurable neurodegenerative disorder that has been linked to various genetic, environmental, and lifestyle factors. Recent research has revealed several potential targets for drug development, such as the prevention of Aβ production and removal, prevention of tau hyperphosphorylation, and keeping neurons alive. Drugs that target numerous ADrelated variables have been developed, and early results are encouraging. This review provides a concise map of the different receptor signaling pathways associated with Alzheimer's Disease, as well as insight into drug design based on these pathways. It discusses the molecular mechanisms of AD pathogenesis, such as oxidative stress, aging, Aβ turnover, thiol groups, and mitochondrial activities, and their role in the disease. It also reviews the potential drug targets, in vivo active agents, and docking studies done in AD and provides prospects for future drug development. This review intends to provide more clarity on the molecular processes that occur in Alzheimer's patient's brains, which can be of use in diagnosing and preventing the condition.
The release of antibiotics has attracted wide attention due to their abuse and discharge. How to remove these emerging contaminants is an urgent need to be solved. In the present study, sludge-based biochar combining chitosan and iron oxide was prepared via municipal sewage sludge. The novel biochar modified with chitosan and iron oxide exhibited satisfying performance in eliminating antibiotics from water. The application of modified biochar combined with activated persulfate (PS) showed a remarkable removal efficiency of 96.98% for tetracycline (TC). Analysis of the surface characteristics of the modified biochar showed the presence of structural defects, dispersed iron oxides, numerous functional groups, a porous structure, and a relatively stable crystal structure. These characteristics contributed significant importance to facilitating the removal/degradation of TC. The investigation indicated that the removal efficiency was maintained at feasible conditions with the treatment process under a low TC concentration (30 mg/L), with a temperature at T = 308.15K, solution pH = 4. Three degradation pathways and seven intermediate products of TC were proposed. Therefore, our study provides a promising approach for developing effective removal of antibiotics pollutants.
Amyloid aggregates are the hallmarks of several disorders, including Huntington's, Parkinson's and Alzheimer's diseases. Compounds that could inhibit amyloid fibril formation and/or reduce their associated neurotoxicity might have therapeutic values for treating the diseases. In this work, bis(Indolyl)phenylmethane (BIPM) has been demonstrated to reduce formation of amyloid fibril by hen egg-white lysozyme (HEWL), and also, the effect of aggregates formed in the presence of compound on spatial learning and memory of rats was assessed using Morris water maze. It was found that the compound dose-dependency inhibited amyloid fibrils formation with the optimum concentration of 50 µm. Our studies have shown that the compound was capable to directly disrupt the oligomerization of HEWL, and the resulting aggregates were non-toxic. Twenty-four male Wistar rats were divided into four groups: control, scopolamine, HEWL and BIPM. Our results indicated that BIPM-treated rats found platform with less distance traveled (n = 6, p < 0.05) and in less time (n = 6, p < 0.01), compared with the lysozyme group. The compound also increased the percentage of time elapsed (n = 6, p < 0.05) and the distance swum (n = 6, p < 0.001) in the target quadrant in the probe test. The extent of histological injury in the hippocampus was determined by Nissl and Congo red staining. A significant (n = 6, p < 0.05) increase in intact neurons and decrease in amyloid plaques were observed in the hippocampal CA1 region of the BIPM group. Our findings imply that BIPM improved spatial learning and memory by inhibiting amyloid fibril-induced neurotoxicity. In addition, we recommend the use of model proteins as an effective tool to explore the Alzheimer’s disease pathogenesis.
Aggregates of beta amyloid peptide are found to occur in brains of AD patients and are formed upon sequential cleavage of the amyloid precursor protein by BACE1 and γ-secretase. Strategies inhibiting either peptide aggregation or the rate limiting enzyme BACE1 have been in demand for its implication in AD therapeutics. The present study is undertaken to mine compounds with dual ability. In this context, some natural compounds that were already predicted as BACE1 inhibitors by our group, were further tested for their activity as aggregation inhibitors. A pharmacophore model built with known antiamyloidogenic compounds was then applied for screening the natural compounds previously predicted as BACE1 inhibitors. Subsequently experimental validation by Thioflavin-T and Aβ-GFP assay filtered four compounds genistein, syringetin, tamarixetin and ZINC53276039. Out of them, ZINC53276039 showed promising antiamyloidogenic activity to act as a potent inhibitor of aggregation. Interestingly, our previous study revealed syringetin and ZINC53276039 to be good BACE1 inhibitors while tamarixetin to be a moderate BACE1 inhibitor. These good to moderate BACE1 inhibitors with moderate to reasonable antiamyloidogenic activity might show potency in reducing the amyloid load of AD brains.
The present study is aimed to evaluate the neuroprotective efficacy of combination of certain antioxidants (vitamin E, vitamin C, á-lipoic acid and stilbene resveratrol) against lindane induced neurotoxicity. For neurotoxicity, one group of animal was given a single dose of lindane at a dose of 40 mg/kg b.w. In another group of animals combination of antioxidants at a dose of 125 mg/kg b.w. (i.e. vitamin E 50mg/kg; vitamin C 50mg/kg; á-lipoic acid 20 mg/kg and stilbene resveratrol 5mg/kg b.w.) were given a day (24 hrs.) before and 1 hr prior to lindane administration. A vehical treated control group and antioxidant control group were also included. Lipid peroxidation (LPO) and glutathione (GSH) levels and the activities of acetylcholinesterase (AChE) and adenosinetriphophatase (ATPase) were measured in cerebrum of mice after 18 hrs of treatment. Lindane treated group showed high LPO (P<0.01), reduction in GSH level, AChE (p<0.001) and ATPase activity (p < 0.01). Pretreatment with antioxidants in lindane treated group restored the above altered parameters significantly. In conclusion, it is suggested that combination of certain antioxidants significantly reverted the lindane induced neurotoxicity.
Cerebral deposition of β-amyloid is a major neuropathological feature in Alzheimer’s disease. Here we show that tetracyclines, tetracycline and doxycycline, classical antibiotics, exhibit anti-amyloidogenic activity. This capacity was determined by the exposure of β 1-42 amyloid peptide to the drugs followed by the electron microscopy examination of the amyloid fibrils spontaneously formed and quantified with thioflavine T binding assay. The drugs reduced also the resistance of β 1-42 amyloid fibrils to trypsin digestion. Tetracyclines not only inhibited the β-amyloid aggregates formation but also disassembled the pre-formed fibrils. The results indicate that drugs with a well-known clinical profile, including activity in the central nervous system, are potentially useful for Alzheimer’s therapy.
A LZHEIMER DISEASE (AD) IS A neurodegenerative disorder characterized by cognitive decline , impaired performance of activities of daily living, and behav-ioral and psychiatric signs and symptoms. Pathological features of AD include intraneuronal neurofibrillary tangles containing abnormally phos-phorylated tau protein, extracellular amyloid plaques containing the pep-tide amyloid, neuronal cell death, and anatomic as well as functional impairment of neurotransmitter systems. 1,2 Alzheimer disease affects approximately 4.5 million people in the United States. 3 Treatments approved by the Food and Drug Administration were previously limited to monotherapy with cholinesterase inhibitors in patients with mild to moderate AD. 2 In Octo-ber 2003, the Food and Drug Administration approved memantine for the treatment of moderate to severe AD; memantine is now available in more than 40 countries worldwide. Memantine, a low-to moderate-affinity, uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist , represents the first member of a new class of medications showing clinical benefit and good tolerability in AD. Although other NMDA receptor modula-tors (eg, milacemide and D-cycloser-ine) have failed in development as Context Memantine is a low-to moderate-affinity, uncompetitive N-methyl-D-aspartate receptor antagonist. Controlled trials have demonstrated the safety and efficacy of memantine monotherapy for patients with moderate to severe Alzheimer disease (AD) but no controlled trials of memantine in patients receiving a cholinesterase inhibitor have been performed. Objective To compare the efficacy and safety of memantine vs placebo in patients with moderate to severe AD already receiving stable treatment with donepezil.
β-Amyloid (Aβ) peptides are the main protein component of the pathognomonic plaques found in the brains of patients with Alzheimer's disease. These heterogeneous peptides adopt a highly organized fibril structure both in vivo and in vitro. Here we use solid-state NMR on stable, homogeneous fibrils of Aβ{sub (10-35)}. Specific interpeptide distance constraints are determined with dipolar recoupling NMR on fibrils prepared from a series of singly labeled peptides containing ¹³C-carbonyl-enriched amino acids, and skipping no more than three residues in the sequence. From these studies, we demonstrate that the peptide adopts the structure of an extended parallel β-sheet in-register at pH 7.4. Analysis of DRAWS data indicates interstrand distances of 5.3 {+-} 0.3 ⫠(mean {+-} standard deviation) throughout the entire length of the peptide, which is compatible only with a parallel β-strand in-register. Intrastrand NMR constraints, obtained from peptides containing labels at two adjacent amino acids, confirm the secondary structural findings obtained using DRAWS. Using peptides with ¹³C incorporated at the carbonyl position of adjacent amino acids, structural transitions from α-helix to β-sheet were observed at residues 19 and 20, but using similar techniques, no evidence for a turn could be found in the putative turn region comprising residues 25-29. Implications of this extended parallel organization for Aβ{sub (10-35)} for overall fibril formation, stability, and morphology based upon specific amino acid contacts are discussed.
NMR studies of amyloid β-peptides (Aβ) in aqueous solution provide a novel way in which to characterize the apparent Alzheimer’s disease-related conformational polymorphism of Aβ. In the aqueous medium, neither of the polypeptides Aβ(1–40)ox or Aβ(1–42)ox (both of which contain a methionine sulfoxide at position 35) is folded into a globular structure, but they both deviate from random coil behavior by local conformational preferences of several short segments along the amino-acid sequence. Differences between the solution structures of Aβ(1–40)ox and Aβ(1–42)ox are indicated only by decreased flexibility of the region from about residue 32 to the C-terminus in Aβ(1–42)ox when compared to Aβ(1–40)ox. The lack of the observation of more extensive conformational differences between the two molecules is intriguing, considering that Aβ(1–42)ox in aqueous solution has much higher plaque-competence than Aβ(1–40)ox.
Alzheimer's disease (AD) is characterized by the deposition of amyloid plaques in the parenchyma and vasculature of the brain. Although previous analytical studies have provided much information about the composition and structure of synthetic amyloid-beta fibrils, there is, surprisingly, a dearth of data on intact amyloid plaques from AD brain. Therefore, to elucidate the structure and detailed composition of isolated amyloid plaque cores, we utilized a high-resolution, nondestructive technique, Raman microscopy. The data are of very high quality and contain detailed information about protein composition and conformation, about post-translational modification, and about the chemistry of metal binding sites. Remarkably, spectra obtained for senile plaque (SP) cores isolated from AD brain are essentially identical both within and among brains. The Raman data show for the first time that the SP cores are composed largely of amyloid-beta and confirm inferences from X-ray studies that the structure is beta-sheet with the additional possibility that this may be present as a parallel beta-helix. Raman bands characteristic of methionine sulfoxide show that extensive methionine oxidation has occurred in the intact plaques. The Raman spectra also demonstrate that Zn(II) and Cu(II) are coordinated to histidine residues in the SP cores, at the side chains' N(tau) and N(pi) atoms, respectively. Treatment of the senile plaques with the chelator ethylenediaminetetraacetate reverses Cu binding to SP histidines and leads to a broadening of amide features, indicating a "loosening" of the beta-structure. Our results indicate that Abeta in vivo is a metalloprotein, and the loosening of the structure following chelation treatment suggests a possible means for the solubilization of amyloid deposits. The results also reveal a direct chemical basis for oxidative damage caused by amyloid-beta protein in AD.
A potential goal in the prevention or therapy of Alzheimer's disease is to decrease or eliminate neuritic plaques composed of fibrillar beta -amyloid (A beta). In this paper we describe N-methyl amino acid containing congeners of the hydrophobic "core domain" of A beta that inhibit the fibrillogenesis of full-length A beta. These peptides also disassemble preformed fibrils of full-length A beta. A key feature of the inhibitor peptides is that they contain N-methyl amino acids in alternating positions of the sequence. The most potent of these inhibitors, termed A beta 16-22m, has the sequence NH(2)-K(Me-L)V(Me-F)F(Me-A)E-CONH(2). In contrast, a peptide, NH(2)-KL(Me-V)(Me-F) (Me-F)(Me-A)-E-CONH(2), with N-methyl amino acids in consecutive order, is not a fibrillogenesis inhibitor. Another peptide containing alternating N-methyl amino acids but based on the sequence of a different fibril-forming protein, the human prion protein, is also not an inhibitor of A beta 40 fibrillogenesis. The nonmethylated version of the inhibitor peptide, NH(2)-KLVFFAE-CONH(2) (A beta 16-22), is a weak fibrillogenesis inhibitor. Perhaps contrary to expectations, the A beta 16-22m peptide is highly soluble in aqueous media, and concentrations in excess of 40 mg/mL can be obtained in buffers of physiological pH and ionic strength, compared to only 2 mg/mL for A beta 16-22. Analytical ultracentrifugation demonstrates that A beta 16-22m is monomeric in buffer solution. Whereas A beta 16-22 is susceptible to cleavage by chymotrypsin, the methylated inhibitor peptide A beta 16-22m is completely resistant to this protease. Circular dichroic spectroscopy of A beta 16-22m indicates that this peptide is a beta -strand, albeit with an unusual minimum at 226 nm. In summary, the inhibitor motif is that of alternating N-methyl and nonmethylated amino acids in a sequence critical for A beta 40 fibrillogenesis, These inhibitors appear to act by binding to growth sites of A beta nuclei and/or fibrils and preventing the propagation of the network of hydrogen bonds that is essential for the formation of an extended beta -sheet fibril.
The three-dimensional structure of amyloid beta peptide (25-35), which has neurotoxic activity, in lithium dodecyl sulfate micelles was determined by two-dimensional 1H NMR spectroscopy with simulated annealing calculations. A total of 20 converged amyloid beta peptide structures were obtained on the basis of 110 experimental constraints, including 106 distance constraints reduced from the nuclear Overhauser effect (NOE) connectivities and four torsion angle (phi) constraints. The atomic root mean square difference about averaged coordinates is 1.04 +/- 0.25 A for the backbone atoms (N, C alpha, C) and 1.39 +/- 0.27 A for all heavy atoms of the entire peptide. The molecular structure of amyloid beta peptide in membrane-mimicking environment is composed of a short alpha helix in the C terminal position. The three residues from the N-terminus are disordered, but the remaining eight C-terminal residues are well-ordered, which is supported by the RMSD values of the C-terminal region, Lys28-Leu34. In this region, the RMS differences from averaged coordinates are 0.26 +/- 0.11 A for the backbone atoms (N, C alpha, C) and 0.77 +/- 0.21 A for all heavy atoms, which is very low compared with those for the entire peptide. The four amino acid residues from the N-terminus are hydrophilic and the other seven amino acid residues in C-terminus are hydrophobic. So, our results show that the C-terminal region of amyloid beta peptide (25-35) is buried in the membrane and assumes alpha-helical structure, whereas the N-terminal region is exposed to the solvent with a flexible structure. This structure is very similar to membrane-mediated structure of substance P previously reported. The three-dimensional structure of a non-neurotoxic mutant of amyloid beta peptide (25-35), where Asn27 is replaced by Ala, in lithium dodecyl sulfate micelles was also determined. The structure is similar to that of the wild type amyloid beta peptide (25-35) in the C-terminal region, but the N-terminal flexible region is different. The structural comparison of amyloid beta peptide (25-35), its non-neurotoxic mutant and substance P gives a structural basis to understand the mechanism of neurotoxicity caused by amyloid beta peptide.
Alzheimer’s β amyloid protein (Aβ) is a 39 to 43 amino acid peptide that is a major component in the neuritic plaques of Alzheimer’s disease (AD). The assemblies constituted from residues 25–35 (Aβ25–35), which is a sequence homologous to the tachykinin or neurokinin class of neuropeptides, are neurotoxic. We used X-ray diffraction and electron microscopy to investigate the structure of the assemblies formed by Aβ25–35 peptides and of various length sequences therein, and of tachykinin-like analogues. Most solubilized peptides after subsequent drying produced diffraction patterns characteristic of β-sheet structure. Moreover, the peptides Aβ31–35 (Ile–Ile–Gly–Leu–Met) and tachykinin analogue Aβ(Phe31)31–35 (Phe–Ile–Gly–Leu–Met) gave powder diffraction patterns to 2.8Å Bragg spacing. The observed reflections were indexed by an orthogonal unit cell having dimensions of a=9.36Å, b=15.83Å, and c=20.10Å for the native Aβ31–35 peptide, and a=9.46Å, b=16.22Å, and c=11.06Å for the peptide having the Ile31Phe substitution. The initial model was a β strand where the hydrogen bonding, chain, and intersheet directions were placed along the a, b, and c axes. An atomic model was fit to the electron density distribution, and subsequent refinement resulted in R factors of 0.27 and 0.26, respectively. Both peptides showed a reverse turn at Gly33 which results in intramolecular hydrogen bonding between the antiparallel chains. Based on previous reports that antagonists for the tachykinin substance P require a reverse turn, and that Aβ is cytotoxic when it is oligomeric or fibrillar, we propose that the tachykinin-like Aβ31–35 domain is a turn exposed at the Aβ oligomer surface where it could interact with the ligand-binding site of the tachykinin G-protein-coupled receptor.